i had some spare time framebyframe accompanied by bad hard to read explanations probably less useful than reading the notes and credits !! i animate straight ahead, instead of keyframing like most people in case you were wondering !!
basically the gist is the absolute most important thing (other than having fun of course) is to make sure you know where the viewers eyes are at! this way you can keep their attention on the most important details and not have awkward looking transitions because you directed the viewers eyes the wrong way last frame. either have the camera move (everything moves in one direction: object slides out and another slides in) or have the focus transform (moves one way then opposite way as a different thing or actually just changes form to the next focus) also, use easing in everything you can think of! and sync your animation to the rhythm it makes it much cooler (more things happen on a beat then off one). and use turbowarp its scratch with onionskinning and transparency and it loads costumes faster ask questions in the comments! i'll try to answer them i hope this was useful :)